Asthma is the most common chronic disease among children and current management focuses on control using medications and avoidance of factors that exacerbate the disease. Exposure to outdoor and indoor air pollutants, including nitrogen dioxide (NO2), which is a byproduct of combustion, has been associated with worsening asthma morbidity. Recent evidence suggests that hourly peak concentrations of ambient NO2 are associated with increases in emergency department visits and hospitalizations in people with asthma, prompting the EPA to modify the NAAQS standard for ambient NO2 to include an hourly concentration limit of 100ppb. Investigations by members of this research group have shown an association between higher mean concentrations of indoor NO2 and worsening respiratory symptoms in Baltimore children with asthma. Combustion sources, such as gas stoves, are unique to the indoor environment and produce short-term peak concentrations of NO2 that are not captured in mean concentrations measured over several days. However, the effect of peak indoor NO2 concentrations on asthma health is unknown. We hypothesize that these peak concentrations contribute to worse asthma and are more strongly linked to respiratory health than daily or weekly averages of NO2 concentrations. To study the effect of short-term and peak NO2 concentrations on asthma symptoms and lung function in children with asthma, we propose to add continuous monitoring of indoor NO2 concentrations and the administration of comprehensive time activity diaries in a subgroup (n=40) of children with asthma already enrolled in an existing study, The Center for Childhood Asthma in the Urban Environment ASTHMA-DIET Study. This proposal has three novel aims. First, to determine whether daily peak indoor NO2 concentrations are associated with asthma morbidity in inner city children, we will examine the effect of daily peak indoor NO2 concentrations on lung function and symptoms in children with asthma. Second, to determine whether daily average indoor NO2 concentrations are associated with asthma morbidity in inner city children, we will examine the relationship between 24-hour average NO2 concentrations and asthma outcomes. Finally, we will use detailed time activity diaries to determine the relative contribution of indoo sources to short-term variability in NO2 concentrations in inner-city homes. Results from this study will identify potential sources of elevated NO2 concentrations and inform whether future intervention studies can be directed at short-term increases in NO2 concentrations, which may be more cost-effective and feasible than strategies aimed at continuous NO2 reduction.